﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;

namespace TOOLS
{
    public class ParameterReplacer : ExpressionVisitor
    {
        public ParameterReplacer(ParameterExpression paramExpr)
        {
            this.ParameterExpression = paramExpr;
        }

        public ParameterExpression ParameterExpression { get; private set; }

        public Expression Replace(Expression expr)
        {
            return this.Visit(expr);
        }

        protected override Expression VisitParameter(ParameterExpression p)
        {
            return this.ParameterExpression;
        }
    }

    public static class PredicateExtensionses
    {
        public static Expression<Func<T, bool>> True<T>() { return f => true; }

        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(exp_left.Body);
            var right = parameterReplacer.Replace(exp_right.Body);
            var body = Expression.And(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
        {
            var candidateExpr = Expression.Parameter(typeof(T), "candidate");
            var parameterReplacer = new ParameterReplacer(candidateExpr);

            var left = parameterReplacer.Replace(exp_left.Body);
            var right = parameterReplacer.Replace(exp_right.Body);
            var body = Expression.Or(left, right);

            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }


        public static Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(Expression<Func<TElement, TValue>> valueSelector,
          IEnumerable<TValue> values)
        {
            var startsWithMethod = typeof(string).GetMethod("StartsWith", new[] { typeof(string) });
            var startWiths = values.Select(value => (Expression)Expression.Call(valueSelector.Body, startsWithMethod, Expression.Constant(value, typeof(TValue))));
            var body = startWiths.Aggregate<Expression>(((accumulate, equal) => Expression.Or(accumulate, equal)));
            var p = Expression.Parameter(typeof(TElement));
            return Expression.Lambda<Func<TElement, bool>>(body, p);
        }
    }
}
